Wednesday, April 24, 2019

Pear Slug Sawfly in Area

Some folks are beginning to notice pear slugs feeding on peach, plum or pear trees in their yard.
These are rather unique-looking insects and this often prompts inquiries.

Pear slugs are shaped like caterpillars and are slimy-looking like slugs, but they are really the larvae of a special type of wasp, known as a sawfly. Pear slugs are often observed feeding on the leaves of plums, peaches, pears, or cherries, and occasionally on apples and crab apples. Fully mature larvae are only about ½ inch long and green to dark-green, but it is not uncommon to have multiple larvae feeding on individual leaves. Usually, they feed on the upper surface of the leaves, leaving behind a network of lacy, brown leaf veins and the epidermis on the underside of the leaf. Although infestations are often light and damage is not usually serious, heavy infestations can cause large areas of dead, brown leaves affecting entire branches or areas of trees, and this level of defoliation can be detrimental.

Often it is too late to treat by the time damage is noticed, because the larvae have matured and pupated. In cases where damaging numbers of pear slugs are present, they can be easily controlled by spraying with an insecticide containing the active ingredient spinosad (GreenLight, Monterey, Bonide, and Ferti-lome all sell this product).

Malathion is an even better choice for peaches and plums if you hope to harvest some of the fruit because malathion will also control plum curculio, which the little weevil that produces those legless white grubs inside the fruit. Gardeners who regularly spray their peaches or plums for plum curculio do not normally have to spray specifically for pear slugs.

See Extension Publication 2858, Disease and Insect Control for Homegrown Peaches and Plums, for more information on pest control in homegrown peaches and plums: